This invention relates to electronic duplicators which can detect the dose of light reflected from an original document and responsively adjust to obtain the corresponding desirous copying results.
The quality of the image obtained with recent electronic duplicators has been increasing. This is attributable to the improvement of the material of the photosensitive drum and toner and mechanical improvement such as those concerning, for instance, the distance between the photosensitive drum and developing device at the time of the development that have been made for improving the image quality.
Recently, automatic exposure devices having the function of permitting the self-diagnosis of the image density of the document by the electronic duplicator itself have been developed.
In such an automatic exposure apparatus, the image density of the document to be copied is detected, and the desired copying results are obtained by varying the illumination intensity (hereinafter also referred to as exposure dose) of the exposure light source so that an image of the corresponding proper image density can be obtained or varying the voltage applied to the photosensitive drum or the bias voltage supplied to the developing device.
Hitherto, it has been in practice to detect the image density of the document by providing a section of illuminating the document and a section for detecting the reflected light. By this method, however, the light dose provided by the illuminating section is likely to be insufficient, and extremely high cost is necessary to provide the necessary light dose.
Further, some electronic duplicators of the light transmitting type or light reflecting type incorporate an element, which detects the image density of the document by detecting light from the document, on the light axis between the document provided in a lens housing section and a photosensitive member. However, while this method is effective for large size electronic duplicators having a large lens housing section, it cannot be adopted in small size electronic duplicators for the lens housing section is too large in size for these duplicators and cannot be reduced.